Slim hole drilling method

ABSTRACT

A slim hole drilling method wherein a wellbore of a diameter no greater than about 6 inches is drilled using a drill pipe rotation rate of at least 500 rpm and rotating the drill pipe with at least one electric motor operably connected to the drill pipe. Drilling power units for carrying out the drilling method which employ at least one electric motor in mechanical connection with the drill pipe for rotating the drill pipe and moving with same as it advances toward and away from the wellbore.

United States Patent Striegler [451 June 20, 1972 [54] SLIM HOLEDRILLING METHOD [72] Inventor: John H. Strlegler, Richardson, Tex.

[73] Assignee: Atlantic Richlleld Company, New York,

[22] Filed: Aug. 19, 1970 [21] Appl.No.: 65,177

[52] U.S.Cl. ..175/$7, 173/1, 173/57, 1 175/170 [51] Int. Cl..... lb3/02 [58] FieldotSeareh ..173/l,57, 163; 175/170, 57, 175/67, 61

[56] References Cited UNITED STATES PATENTS 1,377,575 5/1921 Greve..-....173/57 1,395,706 11/1921 Greve ..173/57 X 3,426,855 2/1969Crookeetal. ..l73/S7 OTHER PUBLICATIONS Rotary Drilling Handbook, page123 by J. E. Brantly, Fifth Edition 1952 Primary Examiner-Emest R.Purser Attorney-Blucher S. Tharp and Roderick W. MacDonald ABSTRACT Aslim hole drilling method wherein a wellbore of a diameter no greaterthan about 6 inches is drilled using a drill pipe rotation rate of atleast 500 rpm and rotating the drill pipe with at least one electricmotor operably connected to the drill pipe. Drilling power units forcarrying out the drilling method which employ at least one electricmotor in mechanical connection with the drill pipe for rotating thedrilll pipe and moving with same as it advances toward and away from thewellbore.

4 Clairm, 5 Drawing Figures P'A'Tl-jNTinJunzo I972 v 3.670.832 SHEET 1or 2 w Q" w I INVENTOR JOHN H. STRIEGLER ATTORNEY BACKGROUND OF THEINVENTION As an exploratory tool, it can be desirable to drill verysmall diameter boreholes, hereinafter referred to as slim hole drilling.Whereas a conventional wellbore may start with a diameter of about 20inches, a slim hole wellbore would start with a diameter of no greaterthan about 6 inches. By drilling small diameter boreholes, largernumbers of exploratory wells canbe drilled more economically. Inaddition, the drilling rig necessary for these smaller diameterboreholes is lighter thereby allowing for more economical moving of therig from one drilling location to another.

With slim hole drilling much greater than conventional rotation ratesfor the drill pipe and bit are employed. Whereas conventional rotarydrilling uses rotation rates no greater than about 350 rpm, and mostusually in the range 50-450 rpm, slim hole drilling is preferablycarried out at no less than about 500 rpm.

l-leretofore in offshore rigs in order to gain more working room on theworking floor of the rig, the rotary table has been replaced by anelectric motor hung in the derrick, US. Pat. No. 3,426,855. However, themethod and equipment used in such a drilling setup was for conventionalsize boreholes drilled at conventional rotation rates and therefore wasnot suggestive for slim hole drilling. Nor was it known whether suchequipment would or could be made to stand up under the unique rotationand vibration conditions encountered only with slim hole drillingtechniques.

SUMMARY OF THE INVENTION It has now been found that slim hole drillingtechniques can be carried out successfully with an electric motor driveby employing a method comprising rotary drilling a wellbore having adiameter no greater than about 6 inches, rotating the drill pipe duringat least part of the drilling procedure at a rate of at least 500 rpm,rotating the drill pipe with at least one electric motor operablyconnected to the drill pipe itself, and moving the electric motor withthe drill pipe as it moves in relation to the wellbore.

The electric motor drilling apparatus utilized for cnventional drillingin an offshore rig was not acceptable as such for slirn hole drillingbecause external air cooling hoses connected to the motor frame slowedmovement of the motor and therefore slowed the drilling process andbecause there was more danger of a cooling failure by breakage of acooling hose.

Accordingly, an electric drilling power unit useful in carrying out themethod of this invention comprises a housing having torque armsextending laterally therefrom, an electric motor carried in the housingas hereinafter described, and at least one fan means carried by thehousing and adjacent to the electric motor, the fan means having aninlet means communicating with the exterior of the housing and an outletmeans directing the output of the fan against the motors stator and arotor.

Another suitable power unit comprises a drill pipe section having atleast one gear means attached thereto, an electric motor for each gearmeans attached to the drill pipe section, the electric motor carryingits own gear for meshing with the gear means attached to the drill pipesection.

In both power units the electric motors are supported in such a manneras to be movable toward and away from the wellbore as the drill pipemoves toward and away from the wellbore.

In another embodiment the power units of this invention are employed inthe rig floor instead of in the air.

Accordingly, it is an object of this invention to provide a new andimproved method for slim hole drilling. It is another object to providenew and improved drilling power units for slim hole drilling methods. Itis another object to provide a method and apparatus whereby electricmotors can be em ployed in slim hole drilling techniques withoutsacrifice in economy or reliability of operation.

Other aspects, objects and advantages of this invention will be apparentto those skilled in the art from this disclosure and the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows an elevation of adrilling rig employing one embodiment of this invention.

FIGS. 2 and 3 are cross sections of a drilling power unit embodying oneaspect of this invention.

FIG. 4 is an elevation of another drilling power unit embodying anotheraspect of this invention.

FIG. 5 shows an elevation of part of the rig of FIG. 1 wherein the powerunit is located in the rig floor.

FIG. 1 shows the earth 1 having a wellbore 2 therein and a section ofdrill pipe 3 extending thereinto. A drilling platform 4 with its workingfloor 5 is disposed over wellbore 2. The derrick 6 sitting on platform 4has, for sake of clarity, been simplified to show only two supportinglegs 7 surmounted by a conventional crown block 8.

Drill pipe 3 extends through an opening in floor 5 and an opening inspider 10 to coupling 11. Spider 10 is employed to hold slips whichsupport the drill pipe in the wellbore when the apparatus above coupling11 is disconnected. A rotary table of a typical drilling rig can also beused for this purpose.

Drilling power unit 12 is described in greater detail hereinafter withrespect to FIGS. 2 and 3. As shown in FIG. 1, power unit 12 comprises ahousing or support means 13 hav ing torque arms 14 extending laterallytherefrom and a hollow electric motor shaft 15, the motor being carriedinteriorlyof housing 13, extending above and below housing 13. Shaft 15is connected to coupling 11 below housing 13 and to coupling 16 abovehousing 13. Coupling 16 is connected to swivel 17 whose bail 18 issupported by hook l9, traveling block 20, and wire cables 21 which aresupported by sheaves in crown block 8.

Torque arms 14 are slideably connected to members 22 which are fixed tofloor 5 and crown block 8 so as to provide fixed members which aresubstantially parallel to but spaced from drill pipe 3 and over whichtorque arm adapters 23 can slide so as to render housing 13 movable withdrill pipe 3 as the pipe advances into or out from wellbore 2. Thetorque arms can follow mechanical tracks or another guide means asdesired.

In operation, power unit 12 is utilized to rotate drill pipe 3 whichcarries any type of rotary drill bit (not shown) at the bottom endthereof. wellbore 2 is thereby drilled deeper until coupling 11 is justabove spider 10. At this time shaft 15 is disconnected from coupling 11,another section of drill pipe attached to the lower end of shafi 15,power unit 12 raised in the derrick by raising hook 19 until the lowerend of the new section of drill pipe can be attached to coupling 11, anddrilling continued until wellbore 2 is deepened so that coupling 11 isagain near the top of spider 10. This sequence of events is thenrepeated until wellbore 2 is drilled to the desired depth. Thus, it canbe seen that power unit 12 is raised and lowered in the derrick a largenumber of times using hook 19 with torque arms 14 following along fixedmembers 22. Fixed members 22 can be wire cables which can be slackenedto move power unit 12 over to connect with a new drill pipe section orcan be any other type of fixed or fixable member as desired.

FIG. 2 shows an elevational cross section of power unit 12 whereinhousing 13 is seen to contain an electric motor having its rotor(armature) 30 fixed to hollow shaft 15 which is rotatable within housing13 by means of combination thrust and radial bearings 31 and 32. Stator33 is carried in housing 13 around rotor 30. Around the exterior ofstator 33 and interiorly of housing 13 are two fan means 34 having airinlet means 35 connected to the exterior of housing 13 as shown in FIG.3 and also having outlet means 36 which direct the outtachment withcoupling means 1 1 and 16. Shaft is hollow in that it contains apassageway 37 connecting one threaded end to the other threaded end sothat drilling mud from gooseneck 24 of FIG. 1 can pass through swivell7, and shaft 15 into drill pipe 3.

Various control steps can be taken with the electric motor which areuseful for slim hole drilling and which can readily be achieved withelectric motors. Desirable controls, one or more of which can beemployed in any particular process, include a motor torque output limit,motor torque output reading device, motor rpm control, forward andreverse rotation by the motor, and a motor torque output limit and motorspeed control for use when threading one drill pipe into another drillpipe or unthreading one drill pipe from another drill pipe.

The particular apparatus useful in carrying out each control step varieswidely depending primarily on whether the motor is an alternatingcurrent motor or a direct current motor and which species of alternatingcurrent or direct current motor is employed. In addition, more than onetype of apparatus can be employed on any given motor to achieve thedesired control steps. All such electrical control apparatus, once givena particular motor, is known in the art and can be readily devised byone skilled in the art.

For example, it is preferred that the electric motor be a direct currentmotor. A particularly preferable type of direct current motor is theshunt type direct current motor which is well-known in the art. Withthis type motor one method by which the torque output can be limited toa desired maximum value is by sensing the field current and armaturecurrent and combining the two values such as by multiplication, theresulting value being representative of the torque output of the motorwhich can then be compared with the maximum desired torque output forthe motor. If the measured value of torque output for the motor is lessthan the maximum set value the motor continues to operate in an openloop fashion unless and until the maximum set torque value is exceeded.When the maximum set torque value is exceeded, conventional apparatussuch as a Thyristor circuit can be used to reduce the armature currentto the motor thereby reducing the torque output of the motor to themaximum set value.

Direct readout of the actual torque output of the motor can beaccomplished by simply employing a conventional ampmeter which registersthe magnitude of the value of the combined, sensed armature current andfield current.

Control of the rotational speed of the shunt type direct current motorcan be achieved simply by varying the armature voltage. With this typemotor, for a given field excitation, speed varies directly with appliedarmature voltage, but by weakening (reducing) the field excitation thesame applied armature voltage will result in a high speed. The fieldexcitation can be weakened in any conventional manner such as byinserting magnetic amplifier controlled reactors on the secondary sideof the transformer supplying the field rectifier.

The reversing step for the shunt type direct current motor can be simplyaccomplished by reversing the current through the shunt field in aconventional manner. The motor can also be reversed in its direction ofrotation by reversing the voltage on the armature. The forward andreverse drives for the motor can be combined with the torque limit andspeed control steps described hereinabove when threading or unthreadingsections of drilling pipe. For example when threading one section ofdrilling pipe into another, a torque limit step can be employed so thatexcessive torque cannot be applied to the pipe joints upon completion ofthe threading step. This avoids risk of damaging or breaking apart thethreaded joint. Similar reasoning applies to unthreading one pipe fromanother in that a torque limit step is used and in combination therewitha speed control is used which decreases the rotational speed of theelectric motor as soon as the torque on the motor decreasessignificantly which is indicative of the two sections of pipe startingto be unthreaded and which avoids acceleration in rotational speed ofthe driven section of pipe after it starts unthreading from the fixedsection of pipe.

Additionally, various warning alarms can be employed as desired. Forexample, a heat sensing device can be employed on the electric motoritself which actuates a light, buzzer, or other alarm when the motorextends the preset maximum temperature. Similar warning controls can beemployed on the motors of fans 34 so that if the current to power unit12 is interrupted the operator is warned of a cooling failure in thepower unit.

FIG. 3 shows a bottom cross-sectional view of power unit 12 along theline III-III of FIG. 2. FIG. 3 shows a pair of fan means 34 having airinlet conduit means 35 open to the atmosphere around the exterior ofhousing 13. Fan means 34 are connected by way of shafts 40 to poweringmotors 41. Electric wires 42 from motors 41 and electric wires 43 fromstator 33 are combined into a single cable bundle which passes throughthe exterior of housing 13 (not shown), up along swivel l7 and alonggooseneck 24 to a power source (not shown) located on the groundsomewhere in the vicinity of platform 4.

By the apparatus of power unit 12, with a plurality of fan meansarranged interiorly of housing 13 and around the electric motor withinhousing 13, the fan means each being in direct and open communicationwith ambient air by means of conduits 35 and each having its outputdirected at the motor on the interior of housing 13, the large andcritical demand for cooling of this motor while operating at high slimhole rotation rates can be met without adverse etfects on the motoritself. Also, only a single energy supply conduit needs to run out ofhousing 13, this line being a single electrical conduit. In this mannerthe need for running one or more air hoses along gooseneck 24 and swivel17 to housing 13 is eliminated and power unit 12 is rendered morereliable since no risk is involved of breaking a cooling air hose byconstant flexing with movement of power unit 13 up and down in derrick6.

Accordingly, power unit 12 provides the critical cooling requirement forthe electric motor under the strenuous slim hole operating conditionsand at the same time is substantially more reliable since there are noflexing parts supply the cooling air to the motor. By use of this unit,there is no risk of an unseen cooling air hose leak, which can causeoverheating and failure of the power unit motor. The cooling demand forthe power unit motor when operating at the high rotational speed of slimhole drilling is great and even a small loss in cooling air cannot betolerated without some adverse overheating of the motor.

FIG. 4 shows drill pipe 3 having two gears 50 attached directly to thedrill pipe section. Two electric motors 51 are supported by individualtorque arms 52 which torque arms are slideably movable along a fixedmember 53. Member 53 can extend between floor 5 and crown block 8 in thesame manner of fixed members 22 in FIG. 1. Each motor 51 carries its owngear means 55 by way of shaft 54, each gear means 55 being enmeshed withone gear 50.

The apparatus of FIG. 4 constitutes a drilling and power unit which canbe used in lieu of power unit 12 of FIG. 1, the upper end of drill pipesection 3 of FIG. 4 being connected by way of coupling 16 to swivel 17of FIG. 1 and the lower end of drill pipe section 3 being connected byway of coupling 1 1 to the remaining drill pipe extending into wellbore2.

In operation, as wellbore 2 is deepened, drill pipe section 3 of FIG. 4moves downwardly and so do motors 51 by way of sliding of torque arms 52along fixed members 53. Of course, if desired, suitable housing can beprovided around the apparatus of FIG. 4 to insure that as drill pipesection 3 moves, motors 51 move without disengaging any of the enmeshedgears 50 and 55. This would be obvious to one skilled in the art and,for sake of simplicity, is not shown. Of course, if desired, a singlemotor 51 operating on a single gear 50 or more than two motors 51operating on more than two gears 50 can be employed. Similarly, morethan one motor can be employed inside housing 13 of power unit 12 ifdesired.

The method of this invention comprises rotary drilling a wellbore havinga diameter no greater than about 6 inches,

preferably from about 2 inches to about 5 inches, rotating the drillpipe during at least part of the drilling at a rate of at least 500 rpm,preferably from about 600 rpm to about 2,000 rpm, rotating the drillpipe with at least one electric motor which is operably connecteddirectly to the drill pipe itself, and moving the one or more electricmotors used to rotate the drill pipe with the drill pipe as it movesrelative to the wellbore.

In FIG. 5 only platform 4 and floor 5 of the rig are shown forsimplicity. in FIG. 5 the power unit 13 is fixed in floor 5 in theopening normally occupied by the rotary table of a conventional rig. Inthis embodiment hollow shaft 15 has its interior adapted to receive anddrive a conventional Kelly 60. For example the interior of shaft 15 canbe square in cross section to allow a square Kelly to pass therethrough.

The upper end of Kelly 60 is connected to swivel 17 in a conventionalmanner. Thus, the rig is operated during drilling in the conventionalmanner except that a power unit of this invention is utilized in lieu ofthe conventional rotary table with the hollow shaft of the directcurrent motor of the power unit driving the Kelly. This rig floorcapability is advantageous in that it is very difiicult to obtain thehigh speed of rotation required for slim hole drilling with mechanicaldrives on a conventional rotary table. For example, it is ditficult toobtain 1,500 rpm with a mechanical drive and even then the drivemechanism does not hold up well or for long.

In FIG. 5 only platform 5 and floor 5 of the rig are shown forsimplicity. in FIG. 5 the power unit 13 is fixed in floor 5 in theopening normally occupied by the rotary table of a conventional rig. Inthis embodiment hollow shafi 15 has its interior adapted to receive anddrive a conventional Kelly 60. For example the interior of shaft 15 canbe square in cross section to allow a square Kelly to pass therethrough.

EXAMPLE A wellbore was drilled using substantially the apparatus shownin FIGS. 1 through 3.

The wellbore had a diameter of substantially 3% inches starting at thebottom of the 4 l6 inch O.D., surface pipe set at 128 feet and extendingdown to 4,186 feet, the total depth of the wellbore. The wellbore wasdrilled using 2 1/16 inch diameter drill pipe and a diamond bit, theelectric motor in housing 13 being a 350 horsepower motor which wasoperated so as to rotate the drill pipe at about 1,500 rpm duringsubstantially all the drilling of the wellbore.

During the drilling, the lifting capacity on hook 19 was adjusted so asto maintain a weight of approximately 8,000 pounds on the drill bitduring rotation at about 1,500 rpm. A conventional water based drillingmud was employed during drilling.

Both fans34 were operated at full capacity of 2,000 cubic feet perminute during drilling and no failure of cooling or overheating of themotor in power unit 12 was encountered during drilling of the entirewellbore.

Reasonable variation and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A slim hole drilling method comprising rotary drilling a wellborehaving a diameter no greater than about 6 inches, rotating the drillpipe during at least part of the drilling at a rate of at least 500 rpm,rotating said drill pipe with at least one shunt type direct currentelectric motor operably connected to said drill pipe, limiting thetorque output of said at least one direct current motor by decreasingthe armature current when a maximum desired torque output of the motoris reached, and moving said at least one electric motor with said drillpipe as said drill pipe moves relative to said wellbore.

2. A method according to claim 1 wherein said wellbore diameter is fromabout 2 to 5 inches and said rotation rate is from about 600 to 2,000rpm.

3. A method according to claim 1 wherein the rotational

1. A slim hole drilling method comprising rotary drilling a wellborehaving a diameter no greater than about 6 inches, rotating the drillpipe during at least part of the drilling at a rate of at least 500 rpm,rotating said drill pipe with at least one shunt type direct currentelectric motor operably connected to said drill pipe, limiting thetorque output of said at least one direct current motor by decreasingthe armature current when a maximum desired torque output of the motoris reached, and moving said at least one electric motor with said drillpipe as said drill pipe moves relative to said wellbore.
 2. A methodaccording to claim 1 wherein said wellbore diameter is from about 2 to 5inches and said rotation rate is from about 600 to 2,000 rpm.
 3. Amethod according to claim 1 wherein the rotational speed of said atleast one direct current motor is controlled by varying the armaturevoltage.
 4. A method according to claim 1 wherein the direction ofrotation of said at least one direct current motor is controlled byreversing the current through the shunt field of said motor.